U.S. patent number 9,783,352 [Application Number 14/375,144] was granted by the patent office on 2017-10-10 for multilayer film comprising cyclic olefin copolymer.
This patent grant is currently assigned to E.I. DU PONT DE NEMOURS AND COMPANY. The grantee listed for this patent is E I DU PONT DE NEMOURS AND COMPANY. Invention is credited to Karlheinz Hausmann, Yves M Trouilhet.
United States Patent |
9,783,352 |
Hausmann , et al. |
October 10, 2017 |
Multilayer film comprising cyclic olefin copolymer
Abstract
Disclosed is a multilayer film structure, comprising, in order,
a puncture resistant layer comprising at least one cyclic olefin
copolymer (COC) and at least one ionomer or polyolefin, a tie layer
and a sealant layer. The structure can be coextruded and can be
prepared using a triple bubble process.
Inventors: |
Hausmann; Karlheinz (Auvernier,
CH), Trouilhet; Yves M (Vesenaz, CH) |
Applicant: |
Name |
City |
State |
Country |
Type |
E I DU PONT DE NEMOURS AND COMPANY |
Wilmington |
DE |
US |
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Assignee: |
E.I. DU PONT DE NEMOURS AND
COMPANY (Wilmington, DE)
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Family
ID: |
47679125 |
Appl.
No.: |
14/375,144 |
Filed: |
January 31, 2013 |
PCT
Filed: |
January 31, 2013 |
PCT No.: |
PCT/US2013/024022 |
371(c)(1),(2),(4) Date: |
July 29, 2014 |
PCT
Pub. No.: |
WO2013/116445 |
PCT
Pub. Date: |
August 08, 2013 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20140370278 A1 |
Dec 18, 2014 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61592870 |
Jan 31, 2012 |
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61592884 |
Jan 31, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C
48/21 (20190201); B29C 48/919 (20190201); B29C
55/023 (20130101); B29C 55/28 (20130101); B29C
48/912 (20190201); B29C 48/9105 (20190201); B65D
65/40 (20130101); B29C 48/91 (20190201); B32B
7/12 (20130101); B32B 27/08 (20130101); B29C
48/10 (20190201); B32B 27/325 (20130101); B32B
27/32 (20130101); B32B 2439/70 (20130101); B29K
2077/00 (20130101); B32B 2307/31 (20130101); B29K
2023/06 (20130101); B29K 2105/0085 (20130101); B29K
2023/0625 (20130101); B29K 2023/38 (20130101); B29C
48/0018 (20190201); B29L 2023/001 (20130101); B29L
2009/00 (20130101); Y10T 428/2826 (20150115); B32B
2307/5825 (20130101); B32B 2307/518 (20130101); B29K
2096/005 (20130101); B29K 2029/04 (20130101); B32B
37/153 (20130101); B32B 2307/7242 (20130101); B32B
27/306 (20130101); B29K 2023/12 (20130101); B29L
2031/712 (20130101); B29C 48/355 (20190201); B29K
2023/14 (20130101); B29K 2023/0633 (20130101); B32B
27/34 (20130101); B32B 2307/516 (20130101); B29K
2023/08 (20130101); B29K 2023/086 (20130101); B29C
48/913 (20190201) |
Current International
Class: |
B29C
47/06 (20060101); B29C 47/00 (20060101); B32B
7/12 (20060101); B32B 27/08 (20060101); B65D
65/40 (20060101); B32B 27/32 (20060101); B29C
47/88 (20060101); B29C 55/02 (20060101); B29C
55/28 (20060101); B32B 27/30 (20060101); B32B
27/34 (20060101); B32B 37/15 (20060101); B29C
47/34 (20060101) |
Field of
Search: |
;428/349 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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101875420 |
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Nov 2010 |
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CN |
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109225 |
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Oct 1974 |
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DE |
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0407870 |
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Jan 1991 |
|
EP |
|
0485893 |
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May 1992 |
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EP |
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0800914 |
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Oct 1997 |
|
EP |
|
1423408 |
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Apr 2006 |
|
EP |
|
1803552 |
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Jul 2007 |
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EP |
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2004-330584 |
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Nov 2004 |
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JP |
|
2011-121628 |
|
Jun 2011 |
|
JP |
|
98/27126 |
|
Jun 1998 |
|
WO |
|
2004/024433 |
|
Mar 2004 |
|
WO |
|
WO 2007/095667 |
|
Aug 2007 |
|
WO |
|
2008/139028 |
|
Nov 2008 |
|
WO |
|
Primary Examiner: Zimmer; Marc
Parent Case Text
This application is the national stage entry of the international
application serial number PCT/US2013/024022, filed Jan. 31, 2013,
which claims priority from U.S. Provisional Application Ser. No.
61/592,870, filed Jan. 31, 2012, and U.S. Provisional Application
Ser. No. 61/592,884, filed Jan. 31, 2012.
Claims
The invention claimed is:
1. A coextruded multilayer film structure comprising, in order, at
least one puncture resistant layer comprising at least one cyclic
olefin copolymer and at least one ionomer or polyolefin; at least
one tie layer; at least one barrier layer consisting essentially of
a layer of ethylene vinyl alcohol copolymer (EVOH) between at least
two layers each independently comprising a polyamide, a cyclic
olefin copolymer or a blend of cyclic olefin copolymer and
polyethylene or polypropylene or ionomer; at least a second tie
layer; at least a second puncture resistant layer comprising at
least one cyclic olefin copolymer and at least one ionomer or
polyolefin; and at least one sealant layer; wherein the film is
either monoaxially oriented or biaxially oriented.
2. The multilayer film structure according to claim 1 wherein the
film structure has a puncture resistance of at least 2 J/mm,
wherein the puncture resistance is measured according to DIN14477
at a speed of 1 mm/min using a rod bearing a spherical ball at its
tip, the rod having a diameter of 2 mm and the spherical ball
having a diameter of 2.5 mm.
3. The multilayer film structure according to claim 1 wherein the
at least one puncture resistant layer comprises at least one cyclic
olefin copolymer and at least one ionomer, at least one cyclic
olefin copolymer and polyethylene, or at least one cyclic olefin
copolymer and polypropylene, the tie layer comprises olefin
homopolymers or copolymers, or ethylene copolymers; and the sealant
layer comprises olefin homopolymers and/or copolymers chosen from
among polyethylene, propylene homopolymers and copolymers, ethylene
copolymers, or mixtures thereof.
4. The multilayer film structure according to claim 1 prepared by a
triple bubble process.
5. The multilayer film structure according to claim 1 wherein the
at least one barrier layer consists essentially of a layer of
ethylene vinyl alcohol copolymer between at least two layers each
independently comprising a polyamide or a blend of cyclic olefin
copolymer and polyethylene or polypropylene or ionomer.
6. The structure according to claim 1, wherein the at least one
barrier layer consists of a layer of EVOH between two layers
comprising a blend of cyclic olefin copolymer and ionomer,
polyethylene or polypropylene, optionally with tie layers between
the layer of EVOH and the layers comprising a blend of cyclic
olefin copolymer and ionomer, polyethylene or polypropylene.
7. The structure according to claim 1, wherein the at least one
barrier layer consists of a layer of ethylene vinyl alcohol
copolymer adjacent to and between two layers comprising a
polyamide.
8. The structure according to claim 1 further comprising an outer
layer comprising a polyamide, polycarbonate, polyester, or
polyolefin.
9. The structure according to claim 1, wherein the puncture
resistant layer comprises from 10 to 99 weight percent of the at
least one cyclic olefin copolymer, based on the total weight of the
puncture resistant layer.
10. A packaging article comprising a coextruded multilayer film
structure as characterized in claim 1.
11. The multilayer film structure according to claim 2 wherein the
film structure has a puncture resistance from 2 to 10 J/mm.
12. The multilayer film structure according to claim 3 wherein the
olefin homopolymers or copolymers comprise polyethylene
homopolymers or copolymers, propylene homopolymers or copolymers,
and the ethylene copolymers comprise ethylene .alpha.-olefin
copolymers, ethylene vinyl acetate copolymers, ethylene alkyl
(meth)acrylate copolymers, or polymers or copolymers modified with
acid, anhydride or epoxide functionalities.
13. The multilayer film structure according to claim 3 wherein the
sealant layer comprises an ethylene (meth)acrylic acid copolymer or
ionomer thereof.
14. The multilayer film structure according to claim 3 wherein the
at least one barrier layer consists essentially of a layer of
ethylene vinyl alcohol copolymer between at least two layers each
independently comprising a polyamide or a blend of cyclic olefin
copolymer and polyethylene or polypropylene or ionomer.
15. The multilayer film structure according to claim 3 wherein the
at least one barrier layer consists of a layer of EVOH between two
layers comprising a blend of cyclic olefin copolymer and ionomer,
polyethylene or polypropylene, optionally with tie layers between
the layer of EVOH and the layers comprising a blend of cyclic
olefin copolymer and ionomer, polyethylene or polypropylene.
16. The multilayer film structure according to claim 3 wherein the
at least one barrier layer consists of a layer of ethylene vinyl
alcohol copolymer adjacent to and between two layers comprising a
polyamide.
17. The multilayer film structure according to claim 3 further
comprising an outer layer comprising a polyamide, polycarbonate,
polyester, or polyolefin.
18. The multilayer film structure according to claim 3 wherein the
polyolefin comprises a polyethylene homopolymer, polyethylene
copolymer, polypropylene homopolymer or polypropylene
copolymer.
19. The multilayer film structure according to claim 3 wherein the
at least one tie layer comprises polyethylene homopolymers or
copolymers, propylene homopolymers or copolymers, ethylene vinyl
acetate copolymers, ethylene alkyl (meth)acrylate copolymers, or
polymers or copolymers modified with acid, anhydride or epoxide
functionalities; and the sealant layer comprises an ethylene
(meth)acrylic acid copolymer or ionomer thereof.
20. A process for manufacturing a coextruded multilayer film
structure, said coextruded multilayer film structure comprising, in
order, at least one puncture resistant layer comprising at least
one cyclic olefin copolymer and at least one ionomer or polyolefin;
at least one tie layer; at least one barrier layer consisting
essentially of a layer of ethylene vinyl alcohol copolymer (EVOH)
between at least two layers each independently comprising a
polyamide, a cyclic olefin copolymer or a blend of cyclic olefin
copolymer and polyethylene or polypropylene or ionomer; and at
least one sealant layer; wherein the coextruded multilayer film
structure is either monoaxially oriented or biaxially oriented;
said process comprising the steps of: coextruding a multilayer film
structure to a coextruded tubular film; cooling the coextruded
tubular film in a first bubble; orienting the coextruded tubular
film under heating in a second bubble to produce an oriented film;
and relaxing the oriented film under heating in a third bubble.
21. The process of claim 20 wherein the oriented film is either
mono-axially oriented or biaxially oriented.
Description
The invention relates to a coextruded multilayer film structure
comprising cyclic olefin copolymer that can be used in packaging
such as in food packaging applications.
BACKGROUND OF THE INVENTION
In the field of packaging, both shrinkable and non-shrinkable
multilayer films designed to hold goods must often fulfill multiple
requirements.
For example, when packaging goods that have sharp edges or
needle-like protrusions, it is important that the multilayer films
used in the packaging of such goods have excellent puncture
resistance.
A solution to such puncture resistance requirements can be provided
by a multilayer film comprising a layer containing polyamide, or
blends thereof. For example, EP1296830 describes a multilayer film
comprising an intermediate layer of polyamide having good puncture
resistance properties, suitable for packaging deep-frozen foods
such as ribs and seafood such as crabs.
On the other hand, such multilayer films must also display other
properties such as the tendency to shrink under the influence of
heat and adopt the form of the packaged good, a property known as
"heat shrink".
In most packaging applications such as shrink bags used for food
and in particular for meat packaging, a "heat shrink" of at least
40% is required, but the inclusion of a polyamide layer to enhance
puncture resistance generally also reduces the tendency of a
multilayer film to shrink under heat, and so a compromise between
these two desirable properties must be struck.
Ionomers are known for their excellent ability to shrink under
heat, and depending on the degree of neutralization of the ionomer,
the "heat shrink" of a multilayer film comprising a layer of
ionomer can reach 50% and even higher values.
However, multilayer films comprising a layer of ionomer have only
moderate puncture resistance compared to similar multilayer
structures that contain stiffer components such as polyamide and
are therefore not used extensively to package sharp or pointy edges
such as meat cuts having salient bone fragments or splinters.
It is believed that blends of polyamide and ionomer would result in
a polymeric material combining the puncture resistance of polyamide
and to heat shrink performance of ionomers, but to a strongly
diminished extent, making such compositions less desirable.
There exists the possibility to combine multiple layers in one film
in order to produce a film combining the advantages of each of the
individual layers, but since the economic cost of such a film
increases with its complexity, this is not always advantageous. In
many cases, multilayer films must be constructed by sequential
lamination operations, which add expense. Furthermore, the
inclusion of stiff polyamide layers in order to increase puncture
resistance leads to complications from an environmental point of
view, since the recycling of such structures is inherently
problematic due to the chemical incompatibility between polyamides
and polyolefins.
Therefore, there exists a need to provide a multilayer film that
combines good puncture resistance and, more importantly high "heat
shrink" properties in one layer, which can be manufactured at low
economic cost, and which can be recycled more easily.
EP1423408 discloses sealant layers comprising blends of ionomers
and cyclic olefin polymers having relatively good puncture
resistance, but is silent on the heat shrink behavior of such
blends in oriented multilayer films.
SUMMARY OF THE INVENTION
The above-mentioned problems are solved by a multilayer film
structure, preferably coextruded instead of laminated, comprising,
in order, at least one puncture resistant layer comprising at least
one cyclic olefin copolymer and at least one ionomer or polyolefin;
at least one tie layer; and at least one sealant layer; wherein the
film is either monoaxially oriented or biaxially oriented and
obtained by a triple bubble process; and the film structure has a
puncture resistance of at least 2 J/mm, wherein the puncture
resistance is measured according to DIN14477 at a speed of 1 mm/min
using a rod bearing a spherical ball at its tip, the rod having a
diameter of 2 mm and the spherical ball having a diameter of 2.5
mm.
The multilayer film structure is obtainable by, or obtained by, a
triple bubble process, and may be either monoaxially oriented or
biaxially oriented.
The triple bubble process allows the manufacturing of these
structures in one step through coextrusion, rather than laminating
a biaxially oriented outer film (e.g. polyester) to the layers
containing COC blends with polyolefins or ionomers. This can
significantly reduce the cost of the packaging film. Also in this
case, the entire film is oriented rather than just selected layers,
allowing for more consistent shrink properties.
The invention also provides a (triple bubble) process for
manufacturing a coextruded multilayer film structure, comprising
coextruding a multilayer film structure to a coextruded tubular
film; cooling the coextruded multilayer tubular film structure in a
first bubble; orienting the coextruded multilayer tubular film
structure under heating in a second bubble to produce an oriented
film; and relaxing the oriented film under heating in a third
bubble; wherein the tubular multilayer film structure comprises at
least one puncture resistant layer as characterized above. That is,
the puncture resistant layer comprises at least one COC and at
least one ionomer or polyolefin. In a preferred process, the
oriented film is either mono-axially oriented or biaxially
oriented.
Furthermore, the invention provides an article, in particular a
packaging article, comprising the above-mentioned multilayer film
structures.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 shows a schematic overview of the triple bubble process of
the invention, as described below.
DETAILED DESCRIPTION
The invention provides a multilayer film structure, preferably
coextruded, comprising, in this order, at least one puncture
resistant layer comprising at least one COC and at least one
ionomer or polyolefin, at least one tie layer and at least one
sealant layer.
A preferred multilayer film structure is one wherein the at least
one puncture resistant layer comprises at least one cyclic olefin
copolymer and at least one ionomer, at least one cyclic olefin
copolymer and polyethylene, or at least one cyclic olefin copolymer
and polypropylene, the tie layer comprises olefin homopolymers
and/or copolymers, preferably polyethylene homopolymers or
copolymers, propylene homopolymers or copolymers, or mixtures
thereof, or ethylene copolymers, preferably ethylene .alpha.-olefin
copolymers, ethylene vinyl acetate copolymers, ethylene alkyl
(meth)acrylate copolymers, or polymers or copolymers modified with
acid, anhydride or epoxide functionalities; and the sealant layer
comprises olefin homopolymers and/or copolymers chosen among
polyethylene, propylene homopolymers and copolymers, ethylene
copolymers, preferably ethylene (meth)acrylic acid copolymers and
their corresponding ionomers, and/or mixtures thereof.
Puncture resistance denotes the relative ability of a material to
inhibit the progression of penetration of a sharp object once it
has been pierced by it. Tests devised to measure puncture
resistance are generally application-specific, covering items such
as roofing, packing materials, protective garments, and
needle-resistant materials. For example, a puncture resistant
material can resist a specific pierce force per unit thickness, by
a 25 gauge needle perpendicular to the material, between 0.1 to 150
N/mm, 0.1 to 100 N/mm, 1 to 50 N/mm, 1 to 20 N/mm, or 1 to 10 N/mm,
50 to 150 N/mm, 50 to 100 N/mm, or in form of a specific energy per
unit thickness in J/mm. Typically it can be from 0.1 to 20 or from
1 to 10 J/mm.
The puncture resistance can be measured according to a DIN14477 or
EN388 test at a speed of 1 mm/min using a rod bearing a spherical
ball at its tip, the rod having a diameter of 2 mm and the
spherical ball having a diameter of 2.5 mm. Preferably, films as
described herein have puncture resistance in this test of at least
2 J/mm, such as from 2 to 10 J/mm, preferably from 3 to 8 J/mm.
The puncture resistant layer of the multilayer film structures
comprises at least one COC and at least one ionomer or polyolefin.
Preferably, the puncture resistant layer of the coextruded
multilayer film structure may be essentially free of polyamides
such as for example semi-crystalline and amorphous polyamides, i.e.
the puncture resistant layer of the coextruded multilayer film
structure may not comprise a polyamide, such as for example
semi-crystalline and amorphous polyamides.
The puncture resistant layer may comprise from 10 to 99, 10 to 40,
to 30, 40 to 95, 55 to 95, or 60 to 95 weight % of the COC, based
on the total weight of the puncture resistant layer.
COC includes copolymers of unsaturated cyclic monomers, and may be
obtained by either chain polymerization of one or more unsaturated
cyclic monomers with one or more unsaturated linear monomer such as
for example ethylene, or may be obtained by ring-opening metathesis
of one or more unsaturated cyclic monomers and subsequent
hydrogenation.
Examples of unsaturated cyclic monomers may be chosen from, without
limitation, norbornene and derivatives thereof such as for example
2-norbornene, 5-methyl-2-norbornene, 5,5-dimethyl-2-norbornene,
5-butyl-2-norbornene, 5-ethylidene-2-norbornene,
5-methoxycarbonyl-2-norbornene, 5-cyano-2-norbornene,
5-methyl-5-methoxycarbonyl-2-norbornene, and 5-phenyl-2-norbornene;
cyclopentadiene and derivatives thereof such as for example
dicyclopentadiene and 2,3-dihydrocyclopentadiene; and combinations
of two or more thereof.
Examples of unsaturated linear monomer may be chosen, without
limitation, from alkenes having 1 to 20, preferably from 1 to 12
carbon atoms, most preferably from 1 to 6 carbon atoms, such as for
example alpha-olefins, for example ethylene, propylene, and
butylene. Other unsaturated linear monomers may be chosen from
1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene,
1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and
1-eicocene, cyclopentene, cyclohexane, 3-methylcyclohexene,
cyclooctene, 1,4-hexadiene, 4-methyl-1,4-hexadiene,
5-methyl-1,4-hexadiene, 1,7-octadiene, dicyclopentadiene,
5-ethylidene-2-norbornene, 5-vinyl-2-norbornene,
tetracyclododecene, 2-methyltetracyclododecene, and
2-ethyltetracyclododecene; or combinations of two or more thereof.
Preferably the unsaturated linear monomer is ethylene.
Examples of COC obtained by chain polymerization of one or more
unsaturated cyclic monomers with one or more unsaturated linear
monomer can include copolymers of ethylene and norbornene, ethylene
to and tetracyclododecene.
COC polymers are generally, or even completely, amorphous, highly
transparent and have very high moisture barrier properties, roughly
twice that of HDPE and five times that of LDPE. COC may be chosen
among cyclic olefin copolymers having a glass transition
temperature (Tg) of from 60 to 150.degree. C. or from 70 to
100.degree. C.
Examples of COC obtained by ring-opening metathesis of one or more
unsaturated cyclic monomers and subsequent hydrogenation can
include hydrogenated polynorbornene.
The COC may be chosen from cyclic olefin copolymers having at least
15, from 15 to 90, or from 15 to 40 mole percent of unsaturated
cyclic monomers.
The cycloolefin polymers can be prepared with the aid of
transition-metal catalysts. Preparation processes are described,
for example, in DD-A-109 225, EP-A-0 407 870, EP-A-0 485 893, U.S.
Pat. Nos. 5,869,586 and 6,068,936, and WO98/27126. Molecular weight
regulation during the preparation can advantageously be effected
using hydrogen. Suitable molecular weights can also be established
through targeted selection of the catalyst and reaction conditions.
Details in this respect are given in the above mentioned
specifications.
Suitable cycloolefin polymers are the products sold under the
trademark Topas.RTM. by Ticona.
The puncture resistant layer may also comprise an ionomer based on
an E/X/Y acid copolymer where E is ethylene, X is a C.sub.3 to
C.sub.8 .alpha.,.beta.-ethylenically unsaturated carboxylic acid,
and Y is an optional comonomer selected from alkyl acrylate and
alkyl methacrylate.
Suitable C.sub.3 to C.sub.8 .alpha.,.beta.-ethylenically
unsaturated carboxylic acids may be chosen, for example, among
methacrylic acid and acrylic acid. The C.sub.3 to C.sub.8
.alpha.,.beta.-ethylenically unsaturated carboxylic acid may be
present in an amount from 2 to 30, 5 to 20, or 12 to 19 weight
percent, based on the total weight of the acid copolymer.
The optional comonomer Y may be present in an amount from 0.1 to
40, 0.1 to 10 weight %, based on the weight of the E/X/Y copolymer,
or to not present at all.
To form the ionomer, the carboxylic acid functionalities present in
the E/X/Y copolymer can be at least partially neutralized to salts
containing one or more alkali metal, transition metal, or alkaline
earth metal cations such as for example sodium, zinc, lithium,
magnesium, or calcium.
Thus, an ionomer may be chosen among E/X copolymers where E is
ethylene and X is methacrylic acid at least partially neutralized
by zinc or sodium.
Suitable polymers for use in the present invention are the ionomers
commercially available under the trademark Surlyn.RTM. from E. I.
du Pont de Nemours and Company (DuPont). Example ionomers include a
copolymer of ethylene with 15% methacrylic acid and a melt flow
index (MFI) of 0.7, 58% neutralized with Zn, and a copolymer of
ethylene, with 10% methacrylic acid and MFI of 1.5, 38% neutralized
with Zn.
The puncture resistant layer may also comprise a polyolefin chosen
among polyethylene homopolymers, polyethylene copolymers,
polypropylene homopolymers or polypropylene copolymers and/or
mixtures thereof.
Non-limiting examples of polyethylene homopolymers and/or
copolymers (wherein ethylene is the major comonomer) suitable for
use as a component of the puncture resistant layer or in tie layers
(described further below) in the coextruded multilayer film
structure are, for example, ultra low density polyethylene (ULDPE),
very low density polyethylene (VLDPE), low density polyethylene
(LDPE), linear low density polyethylene (LLPE), high density
polyethylene (HDPE) or metallocene polyethylene (mPE).
Polyethylene homopolymers and/or copolymers may be made by any
available process known in the art including high pressure gas, low
pressure gas, solution and slurry processes employing conventional
Ziegler-Natta, metallocene, and late transition metal complex
catalyst systems.
Polypropylene homopolymers and/or copolymers such as random
copolymers, block copolymers and terpolymers of propylene include
to copolymers of propylene (wherein propylene is the major
comonomer) with other olefins such as ethylene, 1-butene, 2-butene
and the various pentene isomers, and terpolymers of propylene such
as copolymers of propylene with ethylene and one other olefin, and
random copolymers (statistical copolymers) that have propylene and
the comonomer(s) randomly distributed throughout the polymeric
chain in ratios corresponding to the feed ratio of the propylene to
the comonomer(s). Suitable block copolymers are made up of chain
segments consisting of propylene homopolymer and of chain segments
consisting of, for example, random copolymers of propylene and
ethylene.
Polypropylene homopolymers and/or copolymers can be manufactured by
any known process (e.g., using Ziegler-Natta catalyst, based on
organometallic compounds or on solids containing titanium
trichloride). Block copolymers can be manufactured similarly,
except that propylene is generally first polymerized by itself in a
first stage and propylene and additional comonomers such as
ethylene are then polymerized, in a second stage, in the presence
of the polymer obtained during the first. Because the processes for
making polypropylenes are well known to one skilled in the art, the
description thereof is omitted herein for the interest of
brevity.
The thickness of the puncture resistant layer may depend on the
specific end-use of the coextruded multilayer film structure and
can range from 5 to 60 .mu.m or from 10 to 30 .mu.m. The thickness
of the puncture resistant layer may range from 5 to 90%, 10 to 70%,
or 20 to 50%, of the total thickness of the coextruded multilayer
film structure.
The coextruded multilayer film structure comprises at least one tie
layer. The tie layer serves to adhere the puncture resistant layer
to a sealant layer and/or other adjacent layers. In the case where
the tie layer serves to adhere the at least one puncture resistant
layer to the at least one sealant layer, the tie layer is adjacent
to at least one sealant layer and the puncture resistant layer.
Stated alternatively, the tie layer is sandwiched between the
puncture resistant layer and the sealant layer.
The tie layer may comprise one or more olefin homopolymers and/or
copolymers, as described above. Preferably, the one or more to
olefin homopolymers and/or copolymers are chosen among polyethylene
homopolymers and/or copolymers, propylene homopolymers and/or
copolymers, and/or mixtures thereof.
A noted tie layer comprises one or more ethylene copolymers.
"Ethylene copolymer" refers to a polymer comprising repeat units
derived from ethylene and at least one additional monomer. The
additional monomer may be another .alpha.-olefin, or a monomer with
a polar functional group.
The ethylene copolymers may be chosen among ethylene .alpha.-olefin
copolymers, ethylene vinyl acetate copolymers, ethylene alkyl
(meth)acrylate copolymers such as ethylene methyl (meth)acrylate
copolymers, ethylene ethyl (meth)acrylate copolymers, ethylene
butyl (meth)acrylate copolymers, or combinations of two or more
thereof.
"Alkyl (meth)acrylate" refers to alkyl acrylate and/or alkyl
methacrylate.
In the case where the tie layer comprises an ethylene copolymer,
the ethylene copolymer can be an ethylene .alpha.-olefin copolymer
which comprises ethylene and an .alpha.-olefin of 3 to 20 or 4 to 8
carbon atoms.
The density of the ethylene .alpha.-olefin copolymers can range
from 0.860 g/cm.sup.3 to 0.925 g/cm.sup.3, from 0.860 g/cm.sup.3 to
0.91 g/cm.sup.3, or between 0.880 g/cm.sup.3 to 0.905 g/cm.sup.3.
Resins made by Ziegler-Natta type catalysis and by metallocene or
single site catalysis are included provided they fall within the
density ranges so described. The metallocene or single site resins
useful herein are (i) those which have an I-10/I-2 ratio of less
than 5.63 and an Mw/Mn (polydispersivity) of greater than
(I-10/I-2)-4.63, and (ii) those based which have an I-10/I-2 ratio
of equal to or greater than 5.63 and a polydispersivity equal to or
less than (I-10/I-2)-4.63. The metallocene resins of group (ii) may
have a polydispersivity of greater than 1.5 but less than or equal
to (I-10/I-2)-4.63. Conditions and catalysts which can produce
substantially linear metallocene resins are described in U.S. Pat.
No. 5,278,272. The reference gives full descriptions of the
measurement of the well-known rheological parameters I-10 and I-2,
which are flow values under different load and hence shear
conditions. It also provides details of measurements of the
well-known Mw/Mn ratio to determination, as determined by
gel-permeation chromatography (GPC).
The ethylene copolymers may be ethylene copolymerized with a
monomer comprising a polar functional group such as vinyl acetate
or alkyl (meth)acrylates.
When the tie layer comprises an ethylene vinyl acetate copolymer,
the relative amount of copolymerized vinyl acetate units may be of
from 2 to 40, 10 to 40, 10 to 30, or 15 to 28, weight %, based on
the total weight of the ethylene vinyl acetate copolymer. A mixture
of two or more different ethylene vinyl acetate copolymers may be
used as components of the tie layer in place of a single
copolymer.
Ethylene alkyl (meth)acrylate copolymers are thermoplastic ethylene
copolymers derived from the copolymerization of ethylene comonomer
and at least one alkyl (meth)acrylate comonomer, wherein the alkyl
group contains from one to ten carbon atoms and preferably from one
to four carbon atoms.
When the tie layer comprises an ethylene alkyl (meth)acrylate
copolymer, the relative amount of copolymerized alkyl
(meth)acrylate units may be of from 0.1 to 45, 5 to 35, or 8 to 28
weight percent, based on the total weight of the ethylene alkyl
(meth)acrylate copolymer. An example ethylene alkyl (meth)acrylate
copolymer is a copolymer of ethylene and 16% ethyl acrylate, melt
flow index (MFI) of 1.
The olefin homopolymers and/or ethylene copolymers may be modified
copolymers, meaning that the copolymers are grafted and/or
copolymerized with organic functionalities. Modified polymers for
use in the tie layer may be modified with acid, anhydride and/or
epoxide functionalities. Examples of the acids and anhydrides used
to modify polymers, which may be mono-, di- or polycarboxylic acids
are acrylic acid, methacrylic acid, maleic acid, maleic acid
monoethylester, fumaric acid, itaconic acid, crotonic acid,
itaconic anhydride, maleic anhydride and substituted maleic
anhydride, e.g. dimethyl maleic anhydride or citrotonic anhydride,
nadic anhydride, nadic methyl anhydride, and tetrahydrophthalic
anhydride, or combinations of two or more thereof, maleic anhydride
being preferred.
Where the olefin homopolymer and/or copolymer is acid-modified, it
to may contain from 0.05 to 25 weight percent of an acid, based on
the total weight of the modified polymer.
When anhydride-modified polymer is used, it may contain from 0.03
to 10, or 0.05 to 5 weight percent of an anhydride, based on the
total weight of the modified polymer.
Examples of epoxides used to modify polymers can include
unsaturated epoxides comprising from four to eleven carbon atoms,
such as glycidyl (meth)acrylate, allyl glycidyl ether, vinyl
glycidyl ether and glycidyl itaconate, glycidyl (meth)acrylates
being particularly preferred.
Epoxide-modified ethylene copolymers may contain from 0.05 to 15
weight % of an epoxide, based on the total weight of the modified
ethylene copolymer. Epoxides used to modify ethylene copolymers can
include glycidyl (meth)acrylates. An ethylene/glycidyl
(meth)acrylate copolymer may further contain copolymerized units of
an alkyl (meth)acrylate having from one to six carbon atoms and an
.alpha.-olefin having 1 to 8 carbon atoms. Representative alkyl
(meth)acrylates include methyl (meth)acrylate, ethyl
(meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate,
isobutyl (meth)acrylate, hexyl (meth)acrylate, or combinations of
two or more thereof. Of note are ethyl acrylate and butyl acrylate.
The .alpha.-olefin may be selected from the group of propylene,
octene, butene and hexane, especially propylene.
Modified ethylene copolymers can be modified with acid, anhydride
and/or glycidyl (meth)acrylate functionalities.
Olefin homopolymers and/or copolymers and modified polymers are
commercially available under the trademarks APPEEL.RTM.,
BYNEL.RTM., ELVALOY.RTM. AC and ELVAX.RTM. from DuPont.
Ethylene copolymers can be produced by any means known to one
skilled in the art using either autoclave or tubular reactors (e.g.
U.S. Pat. Nos. 3,404,134, 5,028,674, 6,500,888, 3,350,372, and
3,756,996).
The thickness of the tie layer of the multilayer structure may be
between 1 and 100 .mu.m, 5 and 50 .mu.m, or 5 to 30 .mu.m.
The coextruded multilayer film structure also comprises at least
one to sealant layer. The sealant layer serves to adhere the film
structure to any suitable substrate or to itself, and may comprises
one or more olefin homopolymers and/or copolymers capable of fusion
bonding on and to any suitable substrate or to itself by
conventional means such as heat sealing.
The sealant layer may comprise olefin homopolymers and/or
copolymers chosen among polyethylene, propylene homopolymers and/or
copolymers, ethylene copolymers such as for example ethylene
(meth)acrylic acid copolymers and their corresponding ionomers,
and/or mixtures thereof.
The sealant layer may also include these homopolymers or copolymers
blended with other polymers. For example, a polyethylene may be
blended with polybutylene to provide a sealant with enhanced
peelability.
Of note is a sealant layer comprising at least one ionomer such as
disclosed above. In the multilayer structure, the ionomer in the
sealant layer be the same as that in the puncture resistant layer
or it may be different.
The multilayer film structure may further comprise at least one
barrier layer and wherein said barrier layer is between the at
least one puncture resistant layer and the at least one sealant
layer, preferably wherein the barrier layer comprises ethylene
vinyl alcohol copolymer (EVOH), COC, and blends thereof with
polyethylene, polyvinyl alcohol and polyamides.
When the coextruded multilayer film structure comprises at least
one barrier layer, such barrier layer may be chosen from layers
comprising ethylene vinyl alcohol copolymer (EVOH), COC, and blends
thereof with polyethylene, polyvinyl alcohol and polyamides,
depending on the desired barrier effect (e.g. a moisture barrier
and/or oxygen barrier). Such a barrier layer may be one or more
layers combined.
The coextruded multilayer film structure may also comprise a
barrier layer consisting of a layer of EVOH, which is adjacent to
and between two layers comprising a polyamide or a COC or
comprising a to blend of COC and polyethylene, polypropylene or
ionomer. Stated alternatively, the coextruded multilayer film
structure may also comprise a barrier layer consisting of a layer
of EVOH flanked, on each side, by a layer comprising polyamide,
COC, or a blend of COC and polyethylene, polypropylene or ionomer.
In some embodiments, tie layer(s) may be present between the
barrier layer and the layer comprising polyamide or COC or a blend
of COC and polyethylene, polypropylene or ionomer. Accordingly, a
preferred multilayer film structure is one wherein the at least one
barrier layer consists essentially of a layer of ethylene vinyl
alcohol copolymer between at least two layers each independently
comprising a polyamide or a blend of cyclic olefin copolymer and
polyethylene or polypropylene or ionomer.
A preferred embodiment is the multilayer structure wherein the at
least one barrier layer consists of a layer of ethylene vinyl
alcohol copolymer (EVOH) between two layers comprising a blend of
cyclic olefin copolymer and ionomer, polyethylene or polypropylene,
optionally with tie layers between the layer of EVOH and the layers
comprising a blend of cyclic olefin copolymer and ionomer,
polyethylene or polypropylene.
Another preferred embodiment is the multilayer structure wherein
the at least one barrier layer consists of a layer of ethylene
vinyl alcohol copolymer (EVOH) adjacent to and between two layers
comprising a polyamide.
EVOH polymers generally have an ethylene content of between about
15 mole percent to about 60 mole percent, more preferably between
about 20 to about 50 mole percent. The density of commercially
available EVOH generally ranges from between about 1.12 g/cm.sup.3
to about 1.20 gm/cm.sup.3, the polymers having a melting
temperature ranging from between about 142.degree. C. and
191.degree. C. EVOH polymers can be prepared by well-known
techniques or can be obtained from commercial sources. EVOH
copolymers may be prepared by saponifying or hydrolyzing ethylene
vinyl acetate copolymers. Thus EVOH may also be known as hydrolyzed
ethylene vinyl acetate (HEVA) copolymer. The degree of hydrolysis
is preferably from about 50 to 100 mole percent, more to preferably
from about 85 to 100 mole percent. In addition, the weight average
molecular weight, M.sub.w, of the EVOH component useful in the
structures of the invention, calculated from the degree of
polymerization and the molecular weight of the repeating unit, may
be in the range of 5,000 Daltons to 300,000 Daltons with 50,000 to
70,000 Daltons, such as 60,000 Daltons, being most preferred.
Suitable EVOH polymers may be obtained from Eval Company of America
or Kuraray Company of Japan under the tradename EVAL.TM.. EVOH is
also available under the tradename SOARNOL.RTM. from Noltex L.L.C.
Examples of such EVOH resins include EVAL.TM. F101, EVAL.TM. E105,
EVAL.TM. J102, and SOARNOL.RTM. DT2903, SOARNOL.RTM. DC3203 and
SOARNOL.RTM. ET3803. Preferably the EVOH is orientable from about
3.times.3 to about 10.times.10 stretch without loss in barrier
properties from pinholing, necking or breaks in the EVOH layer.
Of special note are EVOH resins sold under the tradename EVAL.TM.
SP obtained from Eval Company of America or Kuraray Company of
Japan that may be useful as components in the laminated shrink
films of the present invention. EVAL.TM. SP is a type of EVOH that
exhibits enhanced plasticity and that is suited for use in
packaging applications including shrink film. Examples of such EVOH
resins include EVAL.TM. SP 521, EVAL.TM. SP 292 and EVAL.TM. SP
482. The EVAL.TM. SP grades of EVOH are easier to orient than the
conventional EVAL.TM. resins. These EVOH polymers are a preferred
class for use in the multilayer oriented heat shrinkable films of
this invention. Without being bound to theory, it is believed that
the enhanced orientability of the EVAL.TM. SP EVOH resins derives
from their chemical structure, in particular the relatively high
level of head to head adjacent hydroxyl groups in the EVOH polymer
chain. By head to head adjacent hydroxyl groups is meant 1,2-glycol
structural units. By relatively high is meant from about 2 to about
8 mole % 1,2-glycol structural units are present in the EVOH
polymer chain. Preferably, about 2.8 to about 5.2 mole % 1,2-glycol
units will be present.
The barrier layer may comprise EVOH and be sandwiched between two
puncture resistant layers, or stated alternatively, the at least
one barrier layer is adjacent to and between the at least two
puncture resistant to layers.
Accordingly, the multilayer film structure may comprise at least
two puncture resistant layers comprising at least one cyclic olefin
copolymer and at least one ionomer or polyolefin, preferably
wherein the polyolefin is polyethylene or polypropylene; at least
one barrier layer, wherein the at least one barrier layer is
between the at least two puncture resistant layers; at least one
tie layer; and at least one sealant layer.
The multilayer structure may further comprise an outer layer
comprising a polyamide, polycarbonate, polyester, preferably
polyethylene terephthalate, or polyolefin.
The outer layer may give the coextruded multilayer film structure
mechanical resistance and/or printability, and/or may further
comprise one or more additional functional layers such as barrier
layers and/or other functional layers located between the at least
one puncture resistant layer and the at least one sealant
layer.
By outer layer it is meant a layer that is the outermost layer of
the coextruded multilayer film structure, on the face opposite to
that of the sealant layer, i.e. a layer forming the outer face of
the structure on the face opposite to that of the sealant layer.
For example, in a tubular coextruded structure such as that formed
in a triple bubble process, the outer layer is the layer that
serves as the exterior face of the tubular structure. In a package
containing a product, the outer layer is the layer furthest from
the product.
The outer layer may be chosen from polycondensates such as
polyamides, polyesters and polycarbonates or from polyolefins.
Polyamides (abbreviated herein as PA), also referred to as nylons,
are condensation products of one or more dicarboxylic acids and one
or more diamines, and/or one or more aminocarboxylic acids such as
11-aminododecanoic acid, and/or ring-opening polymerization
products of one or more cyclic lactams such as caprolactam and
laurolactam. Polyamides may be fully aliphatic or semiaromatic.
Polyamides from single reactants such as lactams or amino acids,
referred to as AB type polyamides are disclosed in Nylon Plastics
(edited by Melvin L. Kohan, 1973, John Wiley and Sons, Inc.) and
include nylon-6, to nylon-11, nylon-12, or combinations of two or
more thereof. Polyamides prepared from more than one lactam or
amino acid include nylon-6,12.
Other well-known polyamides useful as a component of the outer
layer include those prepared from condensation of diamines and
diacids, referred to as AABB type polyamides (including nylon-66,
nylon-610, nylon-612, nylon-1010, and nylon-1212), as well as from
a combination of lactams, diamines and diacids such as nylon-6/66,
nylon-6/610, nylon-6/66/610, nylon-66/610, or combinations of two
or more thereof.
Fully aliphatic polyamides used in the resin composition are formed
from aliphatic and alicyclic monomers such as diamines,
dicarboxylic acids, lactams, aminocarboxylic acids, and their
reactive equivalents. In this context, the term "fully aliphatic
polyamide" also refers to copolymers derived from two or more such
monomers and blends of two or more fully aliphatic polyamides.
Linear, branched, and cyclic monomers may be used.
Carboxylic acid monomers comprised in the fully aliphatic
polyamides include, but are not limited to aliphatic dicarboxylic
acids, such as for example adipic acid (C6), pimelic acid (C7),
suberic acid (C8), azelaic acid (C9), decanedioic acid (C10),
dodecanedioic acid (C12), tridecanedioic acid (C13),
tetradecanedioic acid (C14), and pentadecanedioic acid (C15).
Diamines can be chosen among diamines with four or more carbon
atoms, including but not limited to tetramethylene diamine,
hexamethylene diamine, octamethylene diamine, decamethylene
diamine, dodecamethylene diamine, 2 methylpentamethylene diamine,
2-ethyltetramethylene diamine, 2 methyloctamethylenediamine;
trimethylhexamethylenediamine, meta-xylylene diamine, and/or
mixtures thereof.
Semi-aromatic polyamides include a homopolymer, a copolymer, a
terpolymer or more advanced polymers formed from monomers
containing aromatic groups. One or more aromatic carboxylic acids
may be terephthalic acid or a mixture of terephthalic acid with one
or more other carboxylic acids, such as isophthalic acid, phthalic
acid, 2-methyl terephthalic acid and naphthalic acid. In addition,
the one or more aromatic carboxylic acids may be mixed with one or
more aliphatic dicarboxylic acids, as disclosed above.
Alternatively, an aromatic diamine such as meta-xylylene diamine
(MXD) can be used to provide a semi-aromatic polyamide, an example
of which is MXD6, a homopolymer comprising MXD and adipic acid.
Preferred polyamides disclosed herein are homopolymers or
copolymers wherein the term copolymer refers to polyamides that
have two or more amide and/or diamide molecular repeat units. The
homopolymers and copolymers are identified by their respective
repeat units. For copolymers disclosed herein, the repeat units are
listed in decreasing order of mole % repeat units present in the
copolymer. The following list exemplifies the abbreviations used to
identify monomers and repeat units in the homopolymer and copolymer
polyamides: HMD hexamethylene diamine (or 6 when used in
combination with a diacid) T Terephthalic acid AA Adipic acid DMD
Decamethylenediamine 6 .epsilon.-Caprolactam DDA Decanedioic acid
DDDA Dodecanedioic acid I Isophthalic acid MXD meta-xylylene
diamine TMD 1,4-tetramethylene diamine 4T polymer repeat unit
formed from TMD and T 6T polymer repeat unit formed from HMD and T
DT polymer repeat unit formed from 2-MPMD and T MXD6 polymer repeat
unit formed from MXD and AA 66 polymer repeat unit formed from HMD
and AA 10T polymer repeat unit formed from DMD and T 410 polymer
repeat unit formed from TMD and DDA 510 polymer repeat unit formed
from 1,5-pentanediamine and DDA 6 polymer repeat unit formed from
.epsilon.-caprolactam 610 polymer repeat unit formed from HMD and
DDA 612 polymer repeat unit formed from HMD and DDDA 11 polymer
repeat unit formed from 11-aminoundecanoic acid 12 polymer repeat
unit formed from 12-aminododecanoic acid
In the art the term "6" when used alone designates a polymer repeat
unit formed from .epsilon.-caprolactam. Alternatively "6" when used
in combination with a diacid such as T, for instance 6T, the "6"
refers to HMD. In repeat units comprising a diamine and diacid, the
diamine is designated first. Furthermore, when "6" is used in
combination with a diamine, for instance 66, the first "6" refers
to the diamine HMD, and the second "6" refers to adipic acid.
Likewise, repeat units derived from other amino acids or lactams
are designated as single numbers designating the number of carbon
atoms.
In various embodiments the polyamide composition comprises one or
more polyamides selected from among the following groups (wherein
PA is shorthand for polyamide or "nylon-"):
Group I polyamides may have semiaromatic repeat units to the extent
that the melting point is less than 210.degree. C. and generally
the semiaromatic polyamides of the group have less than 40 mole
percent of semiaromatic repeat units. Semiaromatic repeat units are
defined as those derived from monomers selected from one or more of
the group consisting of aromatic dicarboxylic acids having 8 to 20
carbon atoms and aliphatic diamines having 4 to 20 carbon atoms.
Notable Group I polyamides include PA6/66, PA6/610, PA6/66/610,
PA6/6T, PA1010, PA1 and PA12.
Group II polyamides have a melting point of at least 210.degree.
C., comprising an aliphatic polyamide such as poly(tetramethylene
hexanediamide) (PA46), poly(.epsilon.-caprolactam) (PA6),
poly(hexamethylene hexanediamide/(.epsilon.-caprolactam) (PA66/6),
poly(hexamethylene hexanediamide) (PA66), poly(hexamethylene
hexanediamide/hexamethylene decanediamide) (PA66/610),
poly(hexamethylene hexanediamide/hexamethylene dodecanediamide)
(PA66/612), poly(hexamethylene hexanediamide/decamethylene
decanediamide) (PA66/1010), poly(hexamethylene decanediamide)
(PA610), poly(hexamethylene dodecanediamide) (PA612),
poly(hexamethylene tetradecanediamide) (PA614), poly(hexamethylene
to hexadecanediamide) (PA616), and poly(tetramethylene
hexanediamide/2-methylpentamethylene hexanediamide) (PA46/D6).
Notable Group II polyamides include PA6, PA66, PA610 and PA612.
Group III polyamides have a melting point of at least 210.degree.
C. and comprise
(aa) 20 to 35 mole percent semiaromatic repeat units derived from
one or more monomers selected from aromatic dicarboxylic acids
having 8 to 20 carbon atoms and aliphatic diamines having 4 to 20
carbon atoms; and
(bb) 65 to 80 mole percent aliphatic repeat units derived from one
or more monomers selected from aliphatic dicarboxylic acids having
6 to 20 carbon atoms and an aliphatic diamine having 4 to 20 carbon
atoms; and lactams and/or aminocarboxylic acids having 4 to 20
carbon atoms. Group III polyamides include poly(tetramethylene
hexanediamide/tetramethylene terephthalamide) (PA46/4T),
poly(tetramethylene hexanediamide/hexamethylene terephthalamide)
(PA46/6T), poly(tetramethylene hexanediamide/2-methylpentamethylene
hexanediamide/decamethylene terephthalamide) PA46/D6/10T),
poly(hexamethylene hexanediamide/hexamethylene terephthalamide)
(PA66/6T), poly(hexamethylene hexanediamide/hexamethylene
isophthalamide/hexamethylene terephthalamide PA66/6I/6T, and
poly(hexamethylene hexanediamide/2-methylpentamethylene
hexanediamide/hexamethylene terephthalamide (PA66/D6/6T). A
preferred Group III polyamide is PA 66/6T.
Group IV polyamides have no melting point and include
poly(hexamethylene isophthalamide/hexamethylene terephthalamide)
(PA6I/6T) and poly(hexamethylene isophthalamide/hexamethylene
terephthalamide/hexamethylene hexanediamide) (PA6I/6T/66).
In various embodiments the polyamide is a Group I polyamide, Group
II polyamide, Group III polyamide, or Group IV polyamide,
respectively.
Of note are polyamides with a lower ratio of methylene units to
amide groups, especially those with a ratio of five or less
methylene units per amide group such as PA6, PA66, PA6/66 and most
especially PA6 and PA66. Also of note are polyamides with a ratio
of methylene units to amide groups of 5 to 9 such as PA612, PA610,
PA612, PA6/610, and PA6/66/610.
Preferred polyamides include PA6, PA66, PA610, PA612, PA6/66,
PA6/610, PA6/66/610, PA6/6T, and combinations thereof. More
preferred polyamides include PA6, PA66, PA610, PA612, and
combinations thereof, with PA6 most preferred.
The polyamides may also be blends of two or more polyamides.
Preferred blends include those selected from the group consisting
of Group I and Group II polyamides, Group I and Group III
polyamides, Group I and Group VI polyamides, Group II and Group III
polyamides, Group II and Group IV polyamides.
Polyamides and processes for making them are well known to those
skilled in the art, so the disclosure of which is omitted in the
interest of brevity.
Suitable polyamides or copolymers thereof may be chosen among
aliphatic or semi-aromatic polyamides including PA6, PA66, PA610,
PA6T, PA6.66, PA10, PA11 or PA12. Of note is a blend of nylon-6 and
nylon-66/610.
Suitable polyesters and copolymers thereof may be chosen among
aliphatic polyesters such as polyhydroxyalkanoic acids like for
example polylactic acid or poly(3-hydroxybutyrate) or among
semi-aromatic polyesters like for example polyethylene
terephthalate and copolymers thereof such as PETG, polytrimethylene
terephthalate, polybutylene terephthalate and polyethylene
naphthalate.
Polyesters and processes for making them are well known to those
skilled in the art, so the disclosure of which is omitted in the
interest of brevity.
Suitable polyolefins for use in the outer layer may be chosen from
various types of polyethylene, polypropylene, polystyrene and
ethylene copolymers, as described above.
Each layer of the coextruded multilayer film structure may
independently further comprise, based on the weight of the layer,
from about 0.0001 to about 20%, modifiers and other additives,
including to without limitation, plasticizers, impact modifiers,
stabilizers including viscosity stabilizers and hydrolytic
stabilizers, lubricants, antioxidants, UV light stabilizers,
antifog agents, antistatic agents, dyes, pigments or other coloring
agents, fillers, flame retardant agents, reinforcing agents,
grafting agents, foaming and blowing agents and processing aids
known in the polymer compounding art; for example antiblock agents
and release agents; and combinations of two or more thereof. These
additives may be present in the polymer compositions of each of the
layers independently in amounts of up to 20, such as 0.01 to 7, or
0.01 to 5, weight %.
Exemplary structures according to this invention may be the
coextruded multilayer structures summarized below. In these
structures, the layers are listed from left to right in order from
outer layer (furthest away from the interior of the package or
tubular structure) to inner layer (closest to the interior of the
package or tubular structure). In these structures, outer layers
include polyethylene terephthalate (PET) or polyamide (PA).
Puncture-resistant layers include blends of cyclic olefin copolymer
and ionomer (COC+IO), blends of cyclic olefin copolymer and
polypropylene (COC+PP) and blends of cyclic olefin copolymer and
polyethylene (COC+PE). A single layer barrier layer may be EVOH.
Multilayer barrier layers include COC+PE/tie/EVOH/tie/COC+PE,
COC+IO/tie/EVOH/tie/COC+IO, COC+PP/tie/EVOH/tie/COC+PP and
PA/EVOH/PA. Sealant layers include polyethylene (PE), and ionomer
(IO). Blends of polyethylene and polybutylene (PE+PB) provide
sealant layers with easier peelability.
PET/tie/PE/COC+IO/tie/EVOH/tie/PE PET/tie/PE/COC+PE/tie/EVOH/tie/PE
PET/tie/PE/COC+PP/tie/EVOH/tie/PE PA/tie/P E/COC+IO/tie/EVOH/tie/P
E PA/tie/PE/COC+PE/tie/EVOH/tie/PE PA/tie/PE/COC+PP/tie/EVOH/tie/PE
PET/tie/PE/COC+IO/tie/EVOH/tie/IO PET/tie/PE/COC+PE/tie/EVOH/tie/IO
PET/tie/PE/COC+PP/tie/EVOH/tie/IO PA/tie/PE/COC+IO/tie/EVOH/tie/IO
PA/tie/PE/COC+PE/tie/EVOH/tie/IO PA/tie/PE/COC+PP/tie/EVOH/tie/IO
PET/tie/COC+IO/COC+PE/tie/EVOH/tie/PE
PET/tie/COC+IO/COC+PP/tie/EVOH/tie/PE
PET/tie/COC+PE/COC+IO/tie/EVOH/tie/PE
PET/tie/COC+PE/COC+PP/tie/EVOH/tie/PE
PET/tie/COC+PP/COC+IO/tie/EVOH/tie/PE
PET/tie/COC+PP/COC+PE/tie/EVOH/tie/PE
PET/tie/COC+IO/COC+PE/tie/EVOH/tie/PE
PET/tie/COC+IO/COC+PP/tie/EVOH/tie/IO
PET/tie/COC+PE/COC+IO/tie/EVOH/tie/IO
PET/tie/COC+PE/COC+PP/tie/EVOH/tie/IO
PET/tie/COC+PP/COC+IO/tie/EVOH/tie/IO
PET/tie/COC+PP/COC+PE/tie/EVOH/tie/IO
PET/tie/COC+IO/COC+PE/tie/EVOH/tie/COC+PE/tie/PE
PET/tie/COC+PP/COC+PE/tie/EVOH/tie/COC+PE/PE
PET/tie/PP/COC+PP/tie/EVOH/tie/COC+PE/PE
PET/tie/PE/COC+PE/tie/EVOH/tie/COC+PE/PE
PET/tie/COC+IO/COC+PE/tie/EVOH/tie/COC+PE/COC+IO/IO
PET/tie/COC+PP/COC+PE/tie/EVOH/tie/COC+PE/COC+PP/IO
PET/tie/COC+IO/tie/PA/EVOH/PA/tie/PE
PET/tie/COC+PP/tie/PA/EVOH/PA/tie/PE
PET/tie/COC+IO/tie/PA/EVOH/PA/tie/PE
PET/tie/COC+IO/tie/PA/EVOH/PA/tie/IO
PET/tie/COC+PP/tie/PA/EVOH/PA/tie/IO
PET/tie/COC+IO/tie/PA/EVOH/PA/tie/IO
PET/tie/PP/COC+PP/tie/PA/EVOH/PA/tie/PE
PET/tie/PE/COC+PE/tie/PA/EVOH/PA/tie/PE
PET/tie/PP/COC+PP/tie/PA/EVOH/PA/tie/IO
PET/tie/PE/COC+PE/tie/PA/EVOH/PA/tie/IO
PET/tie/COC+PP/tie/PA/EVOH/PA/tie/COC+PP/IO
PET/tie/COC+PE/tie/PA/EVOH/PA/tie/COC+PE/IO
PET/tie/COC+IO/tie/PA/EVOH/PA/tie/COC+IO/IO
PET/tie/COC+PP/tie/PA/EVOH/PA/tie/COC+PP/IO
PET/tie/PE/PE+COC/tie/EVOH/tie/PE+COC/PE/PE+PB
PET/tie/PE/PE+COC/tie/EVOH/tie/PE+COC/PE/PE+PB
PET/tie/PE+COC/PE+COC/tie/EVOH/tie/PE+COC/PE/PE+PB
PET/tie/PE+COC/PE+COC/tie/PA/EVOH/PA/tie/PE/PE+PB
PET/tie/Ion/PE+COC/tie/EVOH/tie/PE+COC/PE/PE+PB
PET/tie/Ion+COC/PE+COC/tie/EVOH/tie/PE+COC/PE/PE+PB
PET/tie/PP/PP+COC/tie/EVOH/tie/PE+COC/PE/PE+PB
PET/tie/PP+COC/PE+COC/tie/EVOH/tie/PE+COC/PE+PB
PET/tie/PP+COC/PE+COC/tie/PA/EVOH/PA/tie/PE+COC/PE+PB
PET/tie/PP+COC/PE+COC/tie/PA/EVOH/PA/tie/PE/PE+PB.
In particular embodiments, the ionomer sealant layer and the
COC+IO, COC+PE or the COC+PP layer may further enhance the puncture
resistance and shrinking ability and reduce the tendency of the
coextruded multilayer film structure to curl.
A preferred film structure comprises the layers of PET/tie/puncture
resistant layer/COC+PE/tie/EVOH/tie/COC+PE/tie/PE wherein PET
represents a polyethylene terephthalate outer layer, the puncture
resistant layer comprises a blend of cyclic olefin copolymer and
ionomer or cyclic olefin copolymer and polypropylene, the barrier
layer comprises COC+PE/tie/EVOH/tie/COC+PE, and PE represents a
polyethylene sealant layer.
Another preferred film structure comprises the layers of
PET/tie/puncture resistant
layer/COC+PE/tie/EVOH/tie/COC+PE/puncture resistant layer/IO
wherein PET represents a polyethylene terephthalate outer layer,
each puncture resistant layer independently comprises a blend of
cyclic olefin copolymer and ionomer or cyclic olefin copolymer and
polypropylene, the COC+PE/tie/EVOH/tie/COC+PE is a barrier layer
structure, and IO represents an ionomer sealant layer.
The inventors surprisingly discovered that it is possible to
produce the coextruded multilayer structure by coextrusion and/or
orientation by a triple bubble process. The process can comprise
coextruding at least one puncture resistant layer, at least one tie
layer, and at least one sealant layer to produce a tubular
coextruded multilayer film; cooling the to coextruded tubular
multilayer film structure in a first bubble; orienting (e.g., mono-
or bi-axially) the coextruded tubular multilayer film structure
under heating in a second bubble; and relaxing the oriented
coextruded tubular multilayer film structure under heating in a
third bubble.
In the triple bubble process, the tubular coextruded multilayer
film structure can be heated in the second bubble to a temperature
between the glass transition temperature of the at least one
puncture resistant layer and the melting point of the at least one
puncture resistant layer, such as to a temperature of from 60 to
95.degree. C., or 75 to 95.degree. C.
In the process, the tubular coextruded multilayer film structure
can be heated in the third bubble to a temperature between the
glass transition temperature of the puncture resistant layer and
the melting point of the puncture resistant layer, to a temperature
that is inferior to the temperature in the second bubble, or the
coextruded multilayer film structure can be heated in the third
bubble to a temperature of from 65 to 95.degree. C., or 75 to
95.degree. C., or in the cases of LLDPE to temperatures of 95 to
125.degree. C., or PP to temperatures of 95 to 136.degree. C.
This triple bubble process may allow for the manufacture of
coextruded multilayer film structures comprising at least one
puncture resistant layer having excellent barrier properties as
well as good mechanical properties, excellent heat shrink
performance and transparency.
The step of coextruding the puncture resistant layer, tie layer and
sealant layer may be carried out by connecting multiple feeders
processing the corresponding materials, generally in the form of
granulates, to extruders connected to a circular or annular die to
form a tubular multilayer film in a manner known in the art.
The COC and at least one ionomer or polyolefin of the puncture
resistant layer can be fed into the extruder in the form of a "salt
and pepper blend" by methods known in the art such as to form the
corresponding layer in the tubular coextruded multilayer film.
The polymers making up the tie layer and making up the sealant
layer can be fed into the extruder by methods known in the art such
as to form corresponding layers in the tubular coextruded
multilayer film to structure.
In the case in which the coextruded multilayer film comprises an
outer layer giving the coextruded multilayer film structure
mechanical resistance and/or printability, or comprises one or more
additional functional layers such as barrier layers and/or other
functional layers, the corresponding materials can be fed, in a
manner known in the art, into the extruder by connecting additional
feeders to it and redirecting the melt into the desired areas of
the circular or annular die.
Referring to FIG. 1, a schematic diagram of the triple bubble
process is presented. The first bubble B1 is formed on one end by
the tubular multilayer film structure having a diameter of D1
exiting the circular or annular die of the extruder, and on the
other end by the set of rolls R1 that form the hermetically closed
end of the first bubble B1.
In the first bubble B1, the tubular multilayer film exiting the die
and having an initial diameter D1, is quickly cooled, or quenched,
in a way such as to obtain a minimum amount of crystallization in
the structure.
Said quick cooling, or quenching, is preferably obtained by
quenching the exiting tubular coextruded multilayer film through a
first water bath W1 having a temperature of from 0.1.degree. C. to
50.degree. C., more preferably of from 0.1.degree. C. to 25.degree.
C. and a length of from 0.4 to 5 m, preferably of from 1 to 3 m.
The residence time in the water bath W1 may be adjusted to range of
from 1 to 20 seconds, more preferably from 10 to 20 seconds.
After cooling, the now solidified tubular coextruded multilayer
film structure is then passed through a set of rolls which are
immersed in a second water bath W2 having a temperature of from 60
to 95.degree. C. The second water bath has a variable length of
from 0.4 to 5 meters and the residence time in this bath depending
on the speed of the film line can be from 1 to 20 seconds, more
preferably from 10 to 20 seconds.
The second water bath W2 pre-heats the solidified tubular
coextruded multilayer film passing through to a temperature where
it can be stretched without ripping, of more than 60.degree. C.,
preferably from 60.degree. C. to 95.degree. C., more preferably
from 75.degree. C. and 95.degree. C. In more general terms, the
solidified tubular coextruded multilayer film is heated to a
temperature to above the glass transition temperature of the layer
having the highest glass transition temperature, which in the case
of the present invention is the at least one puncture resistant
layer.
The second water bath W2 may be replaced by or supplemented with
any suitable heating means, such as for example a hot air blower,
an IR heater or heating coils. In the case where the second water
bath W2 is supplemented by a hot air blower, the hot air blower may
be set to a temperature of from 140 to 160.degree. C., which will
heat the tubular coextruded multilayer film to a temperature of
from 75.degree. C. to 95.degree. C. because of the low heat
capacity of air, and the hot air blower is preferably located
immediately after the second set of nip rolls R2 sealing the
upstream (towards the extruder) end of the second bubble.
After being pre-heated in the second water bath W2, the now
softened tubular coextruded multilayer film structure is inflated
to form the second bubble. Forming the softened tubular coextruded
multilayer film structure allows for the structure to be oriented
by drawing in both machine/axial direction (MD) and
transverse/radial direction (TD) in the second bubble B2, at the
same time.
The drawing in the machine/axial direction (MD) can be achieved by
adjusting the speed V2 of a second set of nip rolls R2 that form
the upstream (towards the extruder) end of the second bubble and
the speed V3 of a third set of nip rolls R3 that form the
downstream (away from extruder) end of the second bubble.
Generally, V3 is greater than V2, preferably 2 to 4 times greater
than V2. Stated alternatively, the ratio given by V3N2 is
equivalent to the drawing ratio and is preferably of from 2 to
4.
The drawing in the transverse/radial direction (TD) can be achieved
by adjusting the pressure P1 within the second bubble B2. To adjust
the pressure P1, the distance L1 between a first set of nip rolls
R2 that form the hermetically closed upstream (towards the
extruder) end of the second bubble B2, and a second set of nip
rolls R3 that form the hermetically closed downstream (away from
extruder) end of the second bubble B2 can be adjusted. Reducing the
distance L1 between the two sets of nip rolls to (R2 and R3) will
increase the pressure P1, whereas increasing the distance L1 will
lower the pressure P1 within the second bubble. After drawing in
the transverse/radial direction (TD), the initial diameter D1 of
the softened tubular coextruded multilayer film structure can be
increased to a diameter D2, wherein the ratio between D2 and D1 is
of from 2 to 5, preferably of from 2.5 to 3.5.
While passing through the third set of nip rolls R3, the drawn
tubular coextruded multilayer film structure is flattened to be
more easily conveyed.
After passing through the set of nip rolls R3, the tubular
coextruded multilayer film structure is passed through a fourth set
of nip rolls R4 that form the hermetically closed upstream (towards
the extruder) end of the third bubble B3, and a fifth set of nip
rolls R5 that form the hermetically closed downstream (away from
extruder) end of the third bubble B3.
The fourth and fifth set of nip rolls (R4 and R5) are separated by
a distance L2 that can be adjusted to increase or decrease the
pressure P2 within the third bubble B3 in order to allow the
previously drawn tubular coextruded multilayer film structure to
relax in transverse/radial direction (TD).
Generally, this can be achieved by adjusting the pressure P2 in the
third bubble B3 such that the pressure P2 is lesser than the
pressure P1. The pressure is adjusted by modifying the distance L2
between the fourth and the fifth set of nip rolls (R4 and R5) of
the third bubble B3, which pressure adjustment may modify the
diameter D3. The relaxation ratio is given by the ratio of D3/D2,
whereas D3 is usually lesser than D2 and concurrently the ratio of
D3/D2 is smaller than 1. Typically the ratio of D3/D2 can be of
from 0.8 and 0.95, more preferably between 0.85 and 0.9.
The speed V4 of the fourth set of nip rolls R4 and the speed V5 of
the fifth set of nip rolls may be adjusted in order to allow the
previously drawn tubular coextruded multilayer film to relax in
machine/axial direction (MD).
Generally, this can be achieved by adjusting the speed V5 of the
fifth set of nip rolls R5 such that V5 is lesser than V4. The
relaxation ratio to is given by V5N4, whereas V5 is usually lesser
than V4 and concurrently the ratio of V5N4 is smaller than 1.
Typically the ratio of V5N4 can be of from 0.8 to 0.95, more
preferably of from 0.85 to 0.9.
The temperature of the coextruded multilayer film structure in the
third bubble, the pressure P2 and the ratio of V5N4 may be adjusted
individually or in parallel to achieve a tubular coextruded
multilayer film exhibiting a thermal shrink ranging of from 1 to 60
percent, more preferably of from 30 to 60 percent, in machine/axial
direction (MD) and/or transverse/radial direction (TD), when
measured by immersion of a sample into a water bath at a
temperature of 85.degree. C. for 10 seconds.
The tubular multilayer film is relaxed in the third bubble B3 under
heating. In order to keep the tubular multilayer film at a
temperature of between the glass transition temperature of the at
least one puncture resistant layer and the melting point of the at
least one puncture resistant layer in the second bubble, an
appropriate heating means may be used, such as an IR heater, steam
or heated air heater.
Preferably, the temperature of the coextruded multilayer film
structure in the third bubble B3 is lower than in the second bubble
with the proviso of being between the glass transition temperature
of the at least one puncture resistant layer and the melting point
of the at least one puncture resistant layer.
After passing through the fifth set of nip rolls R5, the tubular
coextruded multilayer film is passed through a set of rolls,
flattened and stored on a roll S.
Optionally, the tubular coextruded multilayer film exiting the
fifth set of nip rolls R5 can be slit on one side by a slitting
knife K to yield a planar coextruded multilayer film that can be
stored on a roll S.
The above process provides for the manufacture of a coextruded
multilayer film comprising at least one, preferably mono- or
bi-axially oriented, puncture resistant layer, at least one tie
layer and at least one sealant layer.
The coextruded multilayer film structure may be used in particular
in packaging applications such as in the manufacture of shrink
bags, but may to also be used in non-packaging applications such as
for example, manufacture of tapes or textiles for building,
landscaping, or garment applications.
The invention further provides for a packaging article comprising a
coextruded multilayer film structure comprising at least one of
mono- or bi-axially oriented puncture resistant layer, at least one
tie layer and at least one sealant layer. In particular, the
packaging article may be used for the packaging of food ingredients
having sharp, pointed and/or cutting edges such as for example
coffee, rice, meat containing bone or bone splinters, or dry
noodles.
The coextruded multilayer film structure may be used in the
packaging article as a lidding film or as a shrink film.
EXAMPLES
Materials used in the Examples set forth below are as follows,
identified by the respective trademarks and trade designations.
PET: polyethylene terephthalate polyester, commercially available
as Lighter C93 from Lighter.
Tie1: ethylene acrylate copolymer, melt flow rate (MFR, determined
according to ASTM D 1238 at 190.degree. C./2.16 kg) of 2,
commercially available as Bynel.RTM. 22E780 from DuPont.
Tie2: LLDPE modified (grafted) with maleic anhydride, commercially
available as Bynel.RTM. 41 E850 from DuPont.
Tie3: maleic anhydride grafted polyolefin commercially available as
Admer.TM. SF730.
PE: low density polyethylene commercially available as LDPE 2420F,
from Dow Chemical Company.
COC: a COC copolymer of ethylene and norbornene with a MFR
(according to ASTM D 1238 at 230.degree. C./2.16 kg) of 6 and a
glass transition temperature (Tg) of 65.degree. C., commercially
available as Topas.RTM. 9506F-500 from TICONA.
PA: nylon-6, commercially available as Grilamid.RTM. F40 from EMS
Chemie.
CoPA: nylon-66/610 copolymer commercially available as Grilon.RTM.
G 20 from EMS Chemie.
CoPP: polypropylene copolymer commercially available as Adsyl.RTM.
6C30F from Lyon-Bassell.
EVOH: ethylene vinyl alcohol copolymer commercially available under
the designation SP2904, from EVAL.
ION1: copolymer of ethylene with 15% methacrylic acid and a melt
flow index (MFI) of 0.7, 58% neutralized with Zn.
mPE: a metallocene catalyzed ethylene-hexene copolymer,
commercially available under the designation Exceed.TM. 2018 from
ExxonMobil Chemical
AB: silicon dioxide antiblock masterbatch containing about 10
weight % silicon dioxide.
Multilayer blown films as summarized in Table 1 and 2 can be
prepared on a triple bubble blown film machine manufactured by
Kuhne Anlagenbau equipped with 11 extruders with gear pumps and
screws with defined but different length/diameter ratios for
different materials. The compositions for each of the layers as
summarized in Tables 1 and 2 were fed to the respective extruders
of the triple bubble extruder. This was a The materials were fed
from separate feeders into separate extruders and coextruded
through an annular die to provide coextruded multilayer films. The
extruders were operated with temperature profiles as follows for
the materials used in the layers.
TABLE-US-00001 Material Feed zone to final zone (left to right) PET
230-260-260-260-260-260-280-280.degree. C. Polyolefins and COCs
185-195-220-220-220-220-220-220.degree. C. PA
250-250-250-250-250-250-250-250.degree. C. EVOH
175-195-200-200-200-200-200-200.degree. C.
The final temperature of the melt in the die was between 250 and
260.degree. C.
A typical blown packaging film was prepared and is summarized in
Table 1 as Comparative Example C1. This structure contained a
polypropylene copolymer core without a barrier layer or a puncture
resistant layer.
TABLE-US-00002 TABLE 1 Comparative Layer Nominal Example (outside
Feed Ratio Thickness C2 to inside) (% of total) (micrometers)
Composition 1 10 6.4 98 PET/2 AB 2 7 4.5 Tie3 3 28 17.9 CoPP 4 4
2.6 CoPP 5 5 3.2 CoPP 6 8 5.1 CoPP 7 6 3.8 CoPP 8 8 5.1 CoPP 9 5
3.2 CoPP 10 4 2.6 Tie3 11 15 9.6 97 ION1/3 AB Puncture Resistance
(J/mm) 1.1-1.4
This film had a relatively low puncture resistance.
Structures containing barrier layers are shown in Table 2. Example
1, a film of the invention, has an identical structure to
Comparative Example C2 except that a polyethylene-COC blend, a
puncture-resistant composition, was used in place of polyethylene
in layers 3 and 4. The extruders were set up to run with the
following output relationship: 7/7/30/6/5/8/6/8/5/3/15 (in %).
TABLE-US-00003 TABLE 2 Comparative Layer Nominal Example Example
(outside to Thickness C2 1 inside) (micrometers) Composition
Composition 1 3 98 PET/2 AB 98 PET/2 AB 2 3 Tie1 Tie1 3 12.6 PE 80
PE/20 COC 4 2.5 PE 80 PE/20 COC 5 2.1 Tie2 Tie2 6 3.4 80 PA/20 CoPA
80 PA/20 CoPA 7 2.5 EVOH EVOH 8 3.4 80 PA/20 CoPA 80 PA/20 CoPA 9
2.1 Tie2 Tie2 10 1.2 80 PE/20 mPE 80 PE/20 mPE 11 6.3 72 PE/15 mPE/
72 PE/15 mPE/ 10 PB/3 AB 10 PB/3 AB Punctures Resistance (J/mm) --
2.2
The resultant films were tested for puncture resistance according
to a DIN14477 or EN388 test at a speed of 1 mm/min using a rod
bearing a spherical ball at its tip, the rod having a diameter of 2
mm and the spherical ball having a diameter of 2.5 mm. In these
tests the rod was placed in contact with the inside layer (layer
11). The results are shown in Tables 1 and 2. Example 1 had good
puncture resistance.
* * * * *